The present invention is directed to heat curable blends of organic epoxy resins and cyclic epoxy siloxane monomers. More particularly, the present invention is directed to heat curable blends of organic epoxy resins and tetraorganotetraepoxy cyclic siloxane monomers which polymerize to form compositions having high heat distortion temperatures.
Blends of epoxy silicones and organic epoxy compounds are known in the art. Reference is made, for example, to U.S. Pat. No. 4,138,255 to Crivello and to copending, commonly assigned application Ser. No. 07/331,219 to Eckberg et al. (Eckberg), filed Mar. 30, 1989.
U.S. Pat. No. 4,138,255 to Crivello discloses a method for effecting the cationic polymerization of an epoxy resin by exposing a mixture of epoxy resin and an aromatic Group VIa onium salt to radiant energy. It is disclosed in Crivello at column 3, line 54 that the epoxy resin may be composed of a mixture of epoxy monomers, epoxy prepolymers, and oxirane containing organic polymers. It is further disclosed at column 4, lines 21-22 that epoxy siloxanes can be used as the epoxy resin.
Copending, commonly assigned application Ser. No. 07/331,219 to Eckberg et al. (Eckberg) discloses a photopolymerizable coating composition containing an organic cycloaliphatic polyepoxide, a cure accelerating amount of a cycloaliphatic epoxy-functional siloxane, and a catalytic amount of a photocatalyst. The photocatalyst can be an aromatic iodonium complex salt.
The present invention is based on the discovery that a polymerizable organic epoxide composition containing certain epoxy siloxane monomers will polymerize to form compositions having heat distortion temperatures which are higher than those obtained for compositions prepared from polymerizable compositions containing organic epoxides alone or in combination with other epoxy siloxane monomers.
The epoxy siloxane monomers used in the invention were disclosed in copending, commonly assigned application Ser. No. 07/391,761 to Crivello et al. (Crivello), filed Aug. 9, 1989. Although Crivello discloses the thermal cationic polymerization of these monomers in the presence of an onium salt and a copper co-catalyst, Crivello does not disclose the combination of these epoxy siloxane monomers with organic epoxide compounds, or the criticality of the amount of onium salt catalyst to the heat distortion temperature of the polymerized composition.